Epidemiologic evidence has been accumulating that cigarette smoking is causally related to cancers of the larynx, oral cavity, and esophagus in both men and women. The mortality ratios for these cancers are similar for smokers of cigarettes, pipes, or cigars. A strong dose-response relationship exists. Compared with those who continue smoking, the risk of cancer decreases for those who quit smoking. Alcohol consumption is also an important risk factor for oral, pharyngeal, laryngeal, and esophageal cancer. The combination of smoking and alcohol acts synergistically to increase risk of these cancers. There is mounting concern about the oral health consequences of the recent resurgence of smokeless tobacco use among teenage boys in the United States. While the evidence is strongest that smokeless tobacco causes cancer of the oral cavity, there is also evidence that the use of smokeless tobacco increases the risk of cancer of the pharynx, larynx, and esophagus. Smokeless tobacco also causes a variety of noncancerous and precancerous oral conditions, the most important of which is oral leukoplakia (other less serious oral conditions associated with the use of smokeless tobacco include gum recession and tooth loss). The purpose of this study is to re-examine the relationships between tobacco use (cigarette smoking and smokeless tobacco) and oral health using recent large national data sets and examine the possible physiologic mechanisms through which tobacco acts on oral tissue.